1. Field of the Invention
This invention relates to illumination control systems and, in particular, feedback control and pulse modulated control of illumination amplifiers.
2. Description of the Prior Art
Control of illumination has been accomplished in the prior art with mechanical devices. The well known aperture and shutter of a camera are common mechanical devices for controlling light. Other prior art illumination control arrangements are described hereafter.
In the photoplotter field, a photohead is used to control light for exposing film. Mechanically positioned filters and shutters are used for illumination control such as described in U.S. Pat. No. 3,330,182 issued in July 1967.
In the construction field; mechanical devices such as shutters, louvres, shades, and awnings are used to control natural illumination. These devices may be fixed or mechanically controlled, but are not provided with electronic control capability.
In the computer field, electronic computers are in wide scale use. Illumination signals must be converted to electronic form for processing in prior art systems because of the absence of illumination computer devices for processing illumination signals.
In the display field, liquid crystal displays require external light, either dependent on ambient light or using light bulbs. Integral illumination sources have not been available for such displays.
Liquid crystal displays provide only fully on or fully off conditions, but do not provide analog or proportional control. Limitations of on-off control arrangements have severly limited applicability of liquid crystal devices. Also, because servo control is related to proportional control, servo control of illumination has not been feasible.
The prior art in illumination control is further defined in the art-of-record of the parent application Ser. No. 366,714 including U.S. Pat. Nos. 3,790,901 to White et al.; 3,778,791 to Lewicki et al.; 3,764,213 to O'Meara; 3,744,906 to Sato et al.; 3,720,923 to Chen et al.; 3,713,042 to Kinsel; 3,705,758 to Haskal; 3,696,344 to Feinleib et al.; 3,670,202 to Paine et al.; 3,558,892 to Seeley; 3,473,084 to Dodge; and 3,427,458 to Parfomak et al. which are herein incorporated-by-reference. The prior art in illumination control is still further defined in the art-of-record of the referenced related applications including U.S. Pat. Nos. 3,836,916 to Wiley; 3,721,164 to Kuttigen; 3,703,858 to Canfora; 3,695,154 to Webster; 3,686,675 to Faul; 3,648,578 to Ritchie; 3,610,119 to Gerber; 3,595,147 to Blattner; 3,565,524 to Pabst et al.; 3,498,711 to Ables et al.; 3,458,253 to Hansen; 3,354,806 to DeLang et al.; 3,330,182 to Gerber et al.; 3,323,414 to Ritchie et al.; and 3,048,093 to Loro which are herein incorporated-by-reference.